How can I constrain a camera to focus on a face of an object?
Lets say you have doing this suggestion :
Constrain camera

But that solution is just make the camera only looking to the center of the object, not the face you want.

The next step you need is just to create a vertex group on the face you want then assign it to the constraint :


Select your target object and go to edit mode.
Select your designed face.
Go to the mesh data tab and in the vertex group field, just add one by click + button.
Rename your vertex group and click assign ( to assign the face you selected )
Then select your camera, go to the constraint tab, and insert your vertex group to the vertex group field